The Dynamic Variation Of Microcystins In Shrimp Ponds And Toxic Mechanism To Litopenaeus Vannamei

The frequent occurrence of cyanobacteria blooms in shrimp ponds has become a prominent problem in shrimp culture,and the microcystins?MCs?produced by cyanobacteria can induce the morbidity and underproduction of Litopenaeus Vannamei?L.Vannamei?.We investigated the dynamic variation and influence factors of MCs in semi-intensive L.Vannamei culture ponds,and explored the toxic mechanism to L.vannamei,the main results were as follows:1.During culture,6 phylums and 43 genu were detected under microscopic examination,including cyanobacteria,chlorophyta,diatoms,cryptophyta,pyrrophyta,euglena.And cyanobacteria were the most abundant in the shrimp ponds,followed by green algae.The dynamic variation,a significant increase after the seedling and then decreased,the later period of culture increased significantly,was suitable for cyanobacteria,toxic Microcystis spp.MCs concentrations and physicochemical factors?NH₄-N,NO₃-N,NO₂-N,PO₄-P,salinity and COD?in water.However,the pH was just the opposite.Correlation analysis and significant test indicated the extremely significant positive correlation between the quantity of cyanobacteria,toxic Microcystis spp.and NH₄-N,NO₃-N,NO₂-N,PO₄-P?P?0.01?,the significant positive correlation between the quantity of cyanobacteria,toxic Microcystis spp.and salinity?P?0.050?The significant positive correlation between the concentration of total MCs and NH₄-N,NO₃-N,NO₂-N,salinity?p?0.05?,and total MCs concentration had significant negative correlation with pH?P?0.01?.2.Median lethal concentration(LC₅₀)of MC-LR and MC-RR to L.Vannamei were 123.21?g/kg,141.48?g/kg respectively with modified Karber's method.After injected,it had great influence on oxidative stress enzymes in L.Vannamei.It increased the enzyme activity of superoxide dismutase?SOD?,glutathione peroxidase?GSH-PX?,peroxidaseactive?POD?to scavenge reactive oxygen species?ROS?,avoidding the damage caused by oxidative stress.Simultaneously,detoxification pathways were promoting with the activities inceasing of acid phosphatase?ACP?,alkaline phosphatase?AKP?,glutathione S transferasecontent?GST?.Apparent damage and apoptosis were observed in the hepatopancreas of the injected shrimp.3.After treated with MC-LR,MC-RR,the synthesis of hemocyanin was significantly increase,its peak came to a head in 8 h.And the expression of hemocyanin mRNA and phenoloxidase gene had a similar tendency.Both of them was involved in resisting from the attack of MCs.Simultaneously,the expression of serine protease inhabitors?SPIs?—serpins gene was remarkably up-regulate,then has effect on proenzyme activating systemshrimp in L.Vannamei.4.Paraffin sections were made and stained with HE after acute poisoned with MC-LR,MC-RR,results showed that the hepatopancreatic tuble was regular arrangement and clear border,however,the expansion and irregular of the hepatopancreatic tuble,vacuole formation were obvious.Analysis of hepatopancreatic cell by flow cytometr showed that the injected shrimp detected the cell apoptosis phenomenon in 16 h.The community of cells appears to drift to the apoptotic region,resulting in the in-defined boundary between living cells and apoptotic cells after 24 h injected MC-LR,MC-RR.5.MC-LR and MC-RR could up-regulate MSTN gene?induce negative regulation of muscle growth?expression,and inhibit expression of RpL18 gene?positive regulation of muscle growth?and E75 gene?related to ecdysteroids?,then affect the muscle growth and molting of L.vannamei.MSTN gene had highly response level to MC-LR,RPL18 gene had highly response level to MC-RR,respectively.